Process for producing furnace black pigments



United States Patent 0 3,383,232 PROCESS FOR PRODUCING FURNACE BLACK PIGMENTS Merrill E. Jordan, Walpole, Hugh J. Deery, Jamaica Plain, Erivan Hagopian, Newton, and Frank R. Williams, Quincy, Mass assignors to Cabot Corporation, Boston, Mass., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 380,679, July 6, 1964. This application Jan. 10, 1966, Ser. No. 519,532

' 6 Claims. (Cl. 106-307) ABSTRACT OF THE DISCLOSURE According to the invention there is disclosed a process for treating certain furnace carbon blacks to produce improved ink grade carbon black pigments, in fluffy form, characterized by having excellent flow properties and a high degree of dispersibility on conventional ink making equipment, said process comprising the steps of treating said furnace blacks with an oxidizing agent more active than molecular oxygen to increase the volatile content of said blacks substantially and then subjecting the sooxidized blacks to fluid energy attrition.

This invention relates to carbon black and is a continuation-in-part of U.S. Ser. No. 380,679, filed July 6, 1964, now abandoned. More precisely, the invention disclosed herein relates to an improved process for producing carbon black pigments for ink systems, especially lithographic ink systems and the like in which carbon black pigments are present in high concentrations.

A continuing problem in the carbon black industry is to provide a suitable carbon black pigment to the ink industry. The most complicating factors inherent in this problem are two: (a) the specialized properties required of the pigment and (b) the physical state in which said pigment is supplied to the ink manufacturer. In general, the most desirable ink pigments are characterized by long flow properties, high jetness or masstone and high tinctorial power. Also since the shear forces most generally utilized in dispersing ink pigments into the proper vehicle are relatively mild, dispersibility is a significant factor. Thus in order to achieve a good dispersion efiiciently in existing equipment, the ink manufacturer requires that the pigment be supplied in as fiuffy a form as practicable.

For many years, channel blacks were used almost exclusively in printing inks. Such blacks were eminently qualified for such an application because in the fluffy form they were readily dispersible and inherently possessed such properties as low particle diameterhence excellent tintorial power-and high volatile contents which contribute to excellent flow characteristics. However, the increasing cost of channel blacks has caused the ink industry in many instances to adopt furnace blacks as substitutes therefor. Today for example, it is estimated that at least about 60% of all news and heatset inks contain furnace blacks as pigments and in such applications fur nace black pigments have generally proved to be entirely satisfactory.

However, the use of furnace blacks as pigments in offset or lithographic inks has left much to be desired. Such inks must possess maximum tinting strength and covering power and thus high loadings of black are normally utilized with amounts up to 20-25% by weight carbon black not being uncommon. At such high concentrations, the flow characteristics of the black are of extreme if not paramount importance. Although there are many known treatments for improving flow characteristics of furnace blacks, the manipulative steps involved therein are generally such that the application of such treatments to furnace blacks usually adversely affects the dispersibility of the ultimate pigment. Thus, the use of a so treated furnace black pigment requires a greater expenditure of energy in order to achieve the stringently high degree of dispersion required in offset or lithographic inks. Accordingly, there is an urgent need in the art for a process which will consistently provide an improved, readily dispersible furnace black pigment in fluffy form which is especially suitable for use in high concentrations in ink vehicles.

A principal object of the present invention is to provide an improved carbon black pigment.

A more specific object of the present invention is to provide an improved process for producing a furnace black in fiuffy form having excellent flow properties and tinting strength together with a high degree of dispersibility which properties especially recommend the black for utility as a pigment in ink vehicles.

Another specific object is to provide an improved process for producing a furnace black pigment which can advantageously be used in high concentrations in those ink systems known to the art as lithographic inks and the ike.

Other objects and advantages of the present invention will in part become obvious to those Well skilled in the art or will in part appear hereinafter.

Broadly, the above-mentioned objects and advantages are realized in accordance with the practice of our invention by a combination of steps in which a furnace carbon black is treated with a selected oxidizing agent and then the oxidized black is subdivided to an especially finelydivided form by a particular attrition process. More specifically, our process involves the steps of first treating a furnace black with an oxidizing agent preferably chosen from the group consisting of nitric acid, nitrogen oxides and ozone to increase the volatile content of said black substantially and then subdividing the so treated black by fluid energy attrition. In accordance with the practice of our invention the resulting product is a furnace black pigment in a fiuffy form having excellent flow properties, high tinctorial power and surprisingly easy dispersibility especially in view of the manner and degree of oxidation imparted thereto.

The principles of our invention are applicable to almost any furnace carbon black. However, the best balance of properties in the final pigmentespecially the most desirable flow characteristicsare obtained when the practice of our invention is applied to furnace blacks whi;h are frequently characterized by those skilled in the art as normal and low structure blacks.

The term structure is difircult to define since structure is a primary property of black which is not strictly influenced consistently by any property or combination of properties. In general the term is used in the art todesignate the degree of aggregation of the primary particles of a black and this property is best observed by electron microscope examination. Since all furnace blacks manifest some degree of aggregation of the primary particles, a particular black is classified as low, normal or high structure depending upon the reative degree of aggregation manifested thereby. The demarcations between the classifications of low, normal and high structure are not well defined. Other properties of a furnace black which are considered by many as indicative of the structure of a black are the conductivity thereof and more especially, the ratio of the oil absorption factor to the average particle diameter. In general, the classification of a black as low, normal, or high structure will vary directly with the value for said ratio. The blacks which we consider especially suitable comprise oil furnace blacks which have a ratio of oil absorption to average electron microscope particle diameter of less than about '6. There are listed in the following table some commercially available blacks of the type which are of particular interest to the present invention: namely, oil furnace blacks having an average electron microscope particle diameter between about and milli-microns, an oil absorption factor between about and 140 pounds of oil per hundred pounds of black and a tinting strength between about 180 and about 240.

4 about 50% or more, preferably from 1.5% to 5%, HNO by Weight of the black and subsequently heating the so treated black at temperatures between about 150 F. and about 400 F. until dry. A sharp increase (usually at least a 100% increase) in volatile content, e.g., to at least about 1.5% by weight of the black, occurs when the black is thus treated. It is to be understood, however,

Sterling R is a. gas furnace carbon black produced by Cabot Corporation having a uigrometcr scale of about 100, a nitrogen surface area of about 23 mfi/gnL, an average particle diameter of about rnillimicrons as determined by electron microscope examination and an oil absorption of about 70 lbs. oil/ lbs.

It is to be understood however, that those blacks listed above as Regal constitute the most preferred embodiment of the present invention. Such furnace blacks as indicated by the ratio of oil absorption to particle diameter have substantially lower than normal structure. These blacks are normally produced in accordance with the teachings set forth in U.S. Patents, 3,010,794 and 3,010,- 795, both to Friauf and Thorley.

The purpose of the first step of the process of our invention, i.e., the oxidation step, is to impart improved fiow characteristics to the furnace blacks of interest. it is well known in the art that in general, the flow characteristics of a carbon black are a direct function of the volatile content. For example, channel blacks inherently manifest excellent long flow characteristics in part because of their high volatile content, e.g., most commercial channel blacks have a volatile content of at least about 5% by weight. Furnace blacks on the other hand rarely manifest such a high volatile content, having in general a percent volatile of about 1% or somewhat less. Accordingly, improved fiow characteristics are usually imparted to furnace blacks by increasing the volatile content thereof, generally by way of oxidation processes in which the furnace black is reacted with oxidizing agents more active than molecular oxygen.

Although many oxidizing agents can be used to impart improved flow characteristics to furnace blacks, we prefer to react said blacks with nitric acid, nitrogen oxides, or ozone. We especially prefer nitric acid as the reactant because of its relative ease of handling, the economic advantages implicit in its use and more particularly because of the more pronounced effectiveness thereof. More espccially, we prefer to treat furnace blacks with an aqueous nitric acid solution. The proportion of solution to black is not especially critical but the amount should be sufiicient to achieve good distribution of the components. For example, under usual mixing conditions, the amount of solution should be at least enough to completely wet the black involved. Generally complete wetting of most blacks can be achieved by the use of approximately an equal amount by weight of acid solution and carbon black but oftentimes, amounts somewhat less, say 10 to 30% of solution by weight of the black, are more desirable. Larger amounts of solution, however, complicate to some extent the subsequent drying of the blacks.

The time of contact of the black with the solution is also not especially critical and will depend to a large extent upon the manner in which the solution and black are mixed. We have found that suitable long flow characteristics may be effectively imparted to the blacks of interest by merely mixing same until uniformly wetted with aqueous nitric acid solutions varying in concentration from about 5% to about 70% HNO or even higher, using proportions sufficient to provide from about 1% to that useful embodiments of the invention also may add less than 100% volatiles to the surface of the black. In many cases, especially at the higher concentrations and proportions of acid, the volatile content of the black can reach as high as 12% or even higher. While, the drying temperature can vary from about F. to about 400 F., temperatures from about 200 F. to about 350 F. are especially preferred. Such temperatures produce satisfactory volatile contents on the black and do not significantly increase the nitrogen surface area or significantly affect the structure properties of the black.

We have found the optimum conditions of treatment with nitric acid includes heating the black and nitric acid at a temperature of about 250 F. until dry.

Many manners of mixing the nitric acid solution with the black and many types of apparatus capable of doing same are within the scope of the present invention. For example, the acid solution may be used in place of the normal pelletizing liquid or otherwise added to a fiulfy black at the time of pelletizing same. Thus, the black may be mixed with the solution in the pelletizing apparatus and thus pelletized and subsequently dried in substantially regular equipment.

Alternative methods of imparting the desired surface characteristics to the blacks of interest involve reacting premoistened or slurried black with nitric acid or nitrogen oxide vapors in suitable concentration and/or proportions at elevated temperatures, e.g., between about 150 F. and about 400 F.

Suitable treatment of the black may also be accomplished by passing unheated mixtures comprising a nitrogen oxide and air over the black while it is slowly rotated in a chamber heated to a temperature above 150 F. and preferably no higher than about 400 F. The black is then subjected to a purge cycle of air in order to remove entrapped or adhering vapors.

The critical surface characteristics for improved flow may also be imparted to furnace blacks by contacting the lack with a stream of freshly generated ozone at about room temperature or slightly higher for a length of time sufiicient to permit interaction between the ozone and the carbon black. The ozone may be prepared by passing air or oxygen through a high voltage silent discharge or over mercury vapor or by any other suitable method. One convenient set of reaction conditions is obtained by contacting a slowly rotating shallow bed of a few inches depth of the black with a gas which contains from about 1% to about 10% by weight ozone. The total amount of ozone required to treat the black may range from about 1 to about 10 lbs. of ozone/100 lbs. black, but usually amounts of from about 2 lbs. to about 8 lbs. ozone/100 lbs. black are preferred. The time of contact will depend upon the concentrations and proportions of ozone and black, but usually times of from about 2 to about 12 hours are sufficient. The temperature should not normally exceed 300 F. and in many cases need be no higher than ambient temperature.

The second step in our process involves subdividing the oxidized furnace black. The manner of subdividing the black is especially critical since mere reduction of the black to a fine aggregate size does not produce the special advantages and benefits which are obtained in accordance with the practice of our invention. We have found that the required degree of dispersibility of the ultimate pigment can only be realized when the subdivision of the oxidized black is achieved by way of fluid energy attrition processes. For the purposes of the present invention, fluid energy attrition processes include those processes wherein the particles to be subdivided are entrained in a fluid medium and attrition thereof is achieved by way of high energy interparticle collisions. In contrast thereto, other fine grinding attrition processes achieve subdivision by way of grinding for example with metal balls or by high energy collision of the particles with solid objects such as rapidly rotating hammers or blades or the like.

We are unable to explain precisely why fluid energy attrition is so advantageous in producing a surprisingly readily dispersible pigment. However, we have found that fluid energy attrition effects some change in surface chemical groups of the oxidized blacks especially when higher temperatures are involved. We are unaware of the exact mechanism by which said changes occur but we feel that said changes are a significant factor which contributes to the advantages to be obtained by the practice of our invention.

The practice of our invention and the advantages to be obtained therefrom will be better understood and appreciated in view of the following specific examples of particular embodiments of our invention. These examples should be considered as illustrative only and in no sense limitive of the scope of the present invention.

EXAMPLE 1 This example compares the performance of representative furnace black pigments treated in accordance with the practice of our invention with the performance of a commercial channel black ink pigment.

SRM-l656, a low structure SAF oil furnace black, was produced in accordance with the teachings set forth in the aforementioned US. patents to Friauf and Thorley. Representative properties of this black include a nigrometer scale of about 79.5, a tinting strength of about 253, an oil absorption factor of about 83 lbs. of oil per 100 lbs. of black and a percent volatile of about 1.3. 250 lbs. of SRM-l656 were well mixed with nitric acid and then rotated at a temperature of 300 F. for 5 hours in a drum dryer at 3 r.p.m. The so treated black had the following properties: a nigrometer scale of 82.3, a tinting strength of about 227, an oil absorption factor of about 64 lbs. of oil per 100 lbs. of black and a percent volatile of 7.2.

Regal 330 is a low structure oil furnace black also produced in accordance with the teachings set forth in the aforementioned US. patents to Friauf and Thorley. Representative properties of Regal 330 include a nigrometer scale of about 85.3, a tinting strength of about 239, an oil absorption factor of about 64 lbs. of oil per 100 lbs. of black and a percent volatile of about 0.65. 250 lbs. of Regal 330 were treated with nitric acid in'the same manner as was the SRM1656. The so treated black had the following properties: a nigrometer scale of about 87.8, a tinting strength of about 223, an oil absorption factor of about 61 lbs. of black and a percent volatile of about 3.42.

A twenty-five gram sample of each of the nitric acid treated SRM-1656 and Regal 330 was mixed with a 75 gram sample of a standard litho vehicle. Even after 6 passes through a three roll mill, the jetness and overall dispersion of the resulting pastes were so poor that neither paste would be acceptable as a commercial ink pigment.

However, in accordance with the practice of our invention, samples of the oxidized SRM-l656 and the oxidized Regal 330 were subdivided by the action of a fluid energy mill. The particular fluid energy mill utilized was a 4" Micronizer, compressed air at room temperature being employed as the grinding fluid. (It is pointed out that normally when a Micronizer is utilized the compressed air is preheated to temperatures of about 600 F. or somewhat higher and thus the conditions employed in this experiment are not the most efficient for fluid energy grinding.)

Twenty-five grams of each of the blacks were then mixed with a 75 gram sample of the same litho vehicle utilized above. For comparative purposes a 25 gram sample of Mogul A was also mixed with a 75 gram sample of said litho vehicle. Mogul A is a long flow commercial channel carbon black which is well known to the art and is used quite extensively as an ink pigment especially in litho systems. 'Each mixture of black and vehicle was given 4 passes on a three roll mill maintained at F. A sample of paste was removed after each pass and said samples were examined for RC. fineness (a measure of dispersibility), flow and wet masstone. The following data was obtained by averaging a large number of runs; additionally it is pointed out that under the carefully controlled conditions of this example a difference of A in the RC. fineness test is considered extremely significant.

TABLE II.P.O. FINENESS TABLE IV.COLOR (FIRST PASS ONLY) Wet Masstone ot Drawdown of Glossy Black Gloss Rating Paper Rating (1 Darkest) (1 Darkest) Oxidized SEW-1656 1 l Mongul A (control) 2 2 It is obvious from the above data that the oxidized furnace blacks produced in accordance with the practice of our invention are superior in performance to a commercial channel black pigment which has enjoyed and still enjoys significant commercial success as an ink pigment. Table II demonstrates that the black-s produced in accordance with the teachings of our invention are more readily dispersible than the channel black. Thus, the RC. fineness values of our pigments are surprisingly high even after only one pass through the three roll mill.

Tables III and IV demonstrate that the flow characteristics and color properties of the furnace black pigments produced in accordance with our invention are also generally superior to those of the commercial channel black pigment.

7 8 MPLE 2 many modifications in the incidental features utilized to illustrate the practice of our invention can be made with- In this example, a direct comparison is made between out departing from the spirit and scope of the present our manner of subdividing the oxidized black (fiuid inv nti energy grinding) and other methods of su division, th re Having described our invention in detail together with being set forth the degree of pigment dispersion obtained preferred embodiments thereof, what we declare as novel in each case. and desire to secure by U.S. Letters Patent is as follows: The oxidized SRMl656 and Regal 330 of Example 1 1. A process for producing an improved ink pigment were subdivided (a) in accordance with the procedure set comprising the steps of:

forth in Example 1 (i.e., by fluid energy) and (b) by (a) contacting a normal to low structure furnace means of two other well known attrition devices, namely carbon black having an electron microscope parthe Mikropulverizer and Mikroatomizer, both of which ticle diameter of between and millimicrons, are classified in the art as high speed hammer mills. an oil absorption factor between about and about Although both of said hammer mills operate on the same 140 pounds of oil/100 pounds of black, and an oil principle, the rotating elements of a Mikroatomizer in- 15 absorption/ average particle diameter ratio of no elude not only hammers but also classifying wheels and greater than about 6 with an oxidizing agent more fans. Both devices are capable of subdividing carb n active than molecular oxygen in an amount and for blacks to an especially fine, generally uniform aggregate a time sufiicient to increase the volatile content of size. A more detailed description of all of the aforemensaid black by at least 100% by weight over the tioned attrition devices may be found on pages l30146 20 original value, and of Chemical Engineering News, Dec. 10, 1962. (b) then passing the so-oxidized black in the dry state Twenty-five grams of each of the blacks subjected t through a high energy fluid energy grinding zone to the various attrition processes were mixed with a gram render said furnace black readily dispersible in ink. sample of a standard litho vehicle. Each mixture was 2. The process of claim 1 wherein said furnace black then given 4 passes on a three roll mill maintained at 25 is a low structure furnace black having an oil absorption about F. Samples of the paste were removed after value below pounds oil/ 100 pounds of carbon black. each pass and RC. fineness determined. The following 3. The process of claim 1 wherein said oxidizing agent data was obtained: is nitric acid.

TABLE V. OXIDIZED V-1656 Pass 1 Pass 2 Pass 3 Pass 4 Specs Scratches Specs Scratches Specs Scratches Specs Scratches Fluid Energy (Microuizer) 8% 9 /2 8% 9V 8% 9% 8% 9% Hammer Mill (Mikrepulverizer) a 4% 9 5 8% 5% 9 5 9 Hammer Mill (M ikroatomizcr) 6% 9 /1 6% 9% 7 9% 7 9% TABLE iv.-oXiDiZED REGAL 330 Pass 1 Pass 2 Pass 3 Pass 4 Specs Scratches Specs Scratches Specs Scratches Specs Scratches Fluid Energy (Micronizer) 8V 9% 9 10 9 10 9% 10 Hammer Mill (Mikropulverizer). 5% 8% 6% 9 7 9 (S34 9 hammer Mill (Mikroatoiuizer) 6% 6% 9% 7% 9% 7% 9% It will be obvious from the RC. fineness values set 4. The process of claim 1 wherein said oxidizing agent forth above that the pigments produced in accordance is anitrogen oxide. with the practice of our invention are surprisingly dis- 5. The process of claim 1 wherein said oxidizing agent persible as compared to pigments produced by means of is ozone. other attrition processes. For example, our pigments mani- 6. The process of claim 1 wherein the oxidation step fest an excellent degree of dispersibility even after only r is accomplished by uniformly mixing the black with a one pass through the three roll mill. In contrast thereto, l n n a ning fr m ab ut 5 to about 70% nitric acid other pigments of approximately th Same aggregate i by weight, and thereafter drying the resultant mixture at but subdivided by way of other attrition processes manitemperatures betWeen about 200 F t a ut 350 F. fest a relatively poor degree of dispersibility. Furthermore, it will be noted that the degree of dispersibility of H References Cited the pigments subdivided by other attrition processes after UNITED STATES PATENTS four passes does not even approach the initial degree of dispersibility of our pigments. The advantages of achiev- 258L448 6/1954 Cmes 2 ing a high degre of dispersibility after only one pass 2,686,107 8/1954 Jordan through a three roll nzill will be obvious to those skilled 3,853,118 2/1962 Bonnet 23 209-1 in the art since the overall efiiciency of ink producing 60 4,092 3/1962 Gessler 23-4092 processes will be greatly benefited. 3 52%? 4/1965 Eckert et 106 307 It is to be understood that althou h 0111 1 low struc- 0 4/1966 Me1( )re at 23-2092 g 3 3,279,935 10/1966 Darnell et al 106-307 ture blacks are involved in the illustrative examples, nevertheless the benefits and advantages which fiow from r the practice of our invention are applicable to any of the TOBIAS LEVOW Pnmwy commercial furnace blacks presently available. Also, S. E. MOTT, Assistant Examiner. 

